T-type Ca and persistent Na currents synergistically elevate ventral, not dorsal, entorhinal cortical stellate cell excitability.

Dorsal and ventral medial entorhinal cortex (mEC) regions have distinct neural network firing patterns to differentially support functions such as spatial memory. Accordingly, mEC layer II dorsal stellate neurons are less excitable than ventral neurons. This is partly because the densities of inhibitory conductances are higher in dorsal than ventral neurons. Here, we report that T-type Ca currents increase 3-fold along the dorsal-ventral axis in mEC layer II stellate neurons, with twice as much Ca3.2 mRNA in ventral mEC compared with dorsal mEC. Long depolarizing stimuli trigger T-type Ca currents, which interact with persistent Na currents to elevate the membrane voltage and spike firing in ventral, not dorsal, neurons. T-type Ca currents themselves prolong excitatory postsynaptic potentials (EPSPs) to enhance their summation and spike coupling in ventral neurons only. These findings indicate that T-type Ca currents critically influence the dorsal-ventral mEC stellate neuron excitability gradient and, thereby, mEC dorsal-ventral circuit activity.